Rolling mill taper control system



Aprxl 8, 1969 R. P. FREEDMAN ETAL 3,436,943

ROLLING MILL TAPER CONTROL SYSTEM L Filed May 20, 1966 3,436,943 ROLLING MILL 'IAPER CQNTROL SYSTEM Robert P. Freedman, Ledyard, and George M. Ketcham,

Mystic, Conn., assignors to General Dynamics Corporation, New York, NX., a corporation of Delaware Filed May 20, 1966, Ser. No. 551,640 Int. Cl. B21b 37/12, 5/14 U.S. Cl. 72-8 4 Claims ABSTRACT F THE DISCLOSURE The present invention relates, generally, to rolling mill control systems, and, more particularly, to a new and improved control system for adjusting the separation of the working rolls of a rolling mill during rolling to provide a tapered product.

Most currently available rolling mill control systems for producing hot or cold rolled material which is tapered in the direction of the rolling use taper rate control or profile control, or a combination of both, as the basis for regulating the separation of the working rolls. A commonly used control system utilizes a taper rate control, effected by controlling the relative speeds of the roll and screwdown motors of a mill, which are, in turn, determined by tachometers, and modilies such control in accordance with the rate of deformation of the mill housing while rolling. While these control systems are accurate and reliable, they are objectionable in many instances because of their cost or diiculty in execution.

Accordingly, it is an object of the present invention to provide a new and improved system for adjusting the working roll separation during the operation of a rolling mill to provide a tapered product utilizing a simple and inexpensive control arrangement.

Another object of the invention is to provide a control system for etfecting control of the taper of a strip of material being rolled which may be used with conventional mill stands without requiring substantial modification of the stands.

These and other objects of the invention are obtained by providing, in a rolling mill having a mill stand including a pair of working rolls supported in a fixed frame and having a control system operatively connected to the stand to vary the separation of the rolls, a device for indicating the length of the material that has passed between the working rolls and producing an electrical signal in accordance therewith, and a computer responsive to the electrical signal for producing and transmitting to the separation control system a further signal representing the working roll separation required to produce a given taper. Preferably the taper control system of the invention also includes an arrangement for varying the taper commanded by the system and, to assure exact control of the roll spacing, the system preferably includes a potentiometer to compensate for changes in the working roll diameter due to wear or other causes. Moreover, in a preferred embodiment, wherein the roll separation control system includes both a Wedge device for making small separation adjustments rapidly and a screwdown device for introducing larger changes in" the roll separation, the taper control system includes an ar- 3,436,943 Patented Apr. 8, 1969 rangement for detecting the end of each pass of the material between the rolls to reset the wedge device to an extreme position. Also, the system may include a device for compensating deiiections in the mill stand resulting from changes in the force constrained in the stand.

Further objects and advantages of the invention will be apparent from a reading of the following description in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating the arrangement of a typical control system according to the invention; and

FIG. 2 is a schematic block diagram illustrating the arrangement of a further component which may be used in conjunction with the system sho-wn in FIG. l.

In the representative rolling mill control system illustrated in FIG. l, a rolling mill stand 9 includes a frame 10 and a pair of working rolls 11 and 12 and corresponding backup rolls 13 and 14, the lower rolls 12 and 14 being mounted in fixed position in the frame 10 of the stand and the working roll 11 and support roll 13 being capable of vertical motion in the stand frame. As in conventional stands, a strip or sheet 15 of steel or the like which is to be rolled passes between the working rolls 11 and 12. Moreover, the working rolls separation control system is of the type described in the Barnikel et al. U.S. application Ser. No. 405,749, tiled Oct. 22, 1964, now Patent No. 3,355,925, for System for Dynamically Adjusting the Working Roll Separation in Rolling Mills and includes an adjusting device 16 for rapid roll separation adjustments comprising a hydraulic ram 17 and a ram-actuated wedge 18 which is mounted between the upper backup roll 13 and a lixed wedge 19 at the upper end of the stand frame 10. Accordingly, the ram drives the wedge in the proper direction to force the upper backup roll 13 and working roll 11 toward the lower rolls in response to a force control signal supplied to it through a line 20. In addition, the stand includes a conventional screwdown arrangement 21 for accomplishing larger roll separation adjustments at a slower speed.

In order to calculate the force to be applied to the rolls to produce a desired taper in the strip 15 automatically and supply a control signal to the adjusting device 16 through the line 20, the control system includes a computer 22 and a digital-to-analog converter 23 which make the necessary computations in the manner described below based on information received from a counter 24 and a pulse tachometer 25 mechanically connected to the lower work roll 12. The tachometer provides voltage output pulses at intervals dependent upon the motion of the working roll 12 so that each of the tachometers voltage output pulses signifies that the roll has rotated a predetermined number of degrees, and thus for a given diameter of the roll, each pulse also signilies that an increment of length of steel has passed between the rolls.

The computer 22 is arranged in any well known manner to calculate, at every position of the strip 15 as it passes between the rolls, the amount of force which must be applied to the working rolls 11 and 12 to produce a pressure on the strip which will result in the strip thickness at that position which is required to impart the desired taper as the strip passes through the mill. These calculations are based on the following equation and reasoning (T2-T1) (Tri-T1) Taper-T where Tzzthickness of the thick end of the strip T1=thickness of the thin end of the strip K=a constant representing the ratio of the Volume of the strip to the width of the strip When the ratio of the thickness of a strip to its length is very small, as in the cases here concerned, urther reduction in the thickness results in elongation of the strip but the width does not increase significantly. Therefore, the ratio of volume (V) to width (W) is a constant, i.e., V/ W=K.

In practice, a strip is passed between the working rolls several times so that the thickness reduction accomplished during each pass is relatively small. Prior to each pass of the strip through the mill stand 9, the input data T1, T2 and K, representing the conditions to be produced by that pass, are fed into the computer 22 which comprises two summing amplifiers 26 and 27, an inverter 28, and two dividing networks 29 and 30. As shown schematically in the drawing, the input data T2 and T1 are added in amplifier 26 and the output of this amplifier (Tz-l-Tl) plus the input datum 2K are then fed into the divider 29. Meanwhile, the output of the inverter 28 (-T1) is added with the input datum T2 in amplifier 27. Finally, the outputs of the divider 29 2K Trl-T1 and the amplifier 27 (T2-T1) are fed into the divider 30 and the output of the divider 30 which is a constant output voltage representing the desired taper is applied to a potentiometer 31. The setting of this potentiometer allows the system to be compensated for changes in roll diameter due to Wear or other causes.

As previously mentioned, each of the voltage output pulses from the tachometer 25 signifies that an increment of length of the strip 15 has passed between the rolls 11 and 12. When a normally closed contact 32 of a relay 33 is closed, the counter 24 receives these voltage output pulses from the tachometer and advances lone position for each pulse.

The output from the counter 24 is converted to analog form by the digital-to-analog converter 23 and is multiplied with the taper signal received from the potentiometer tap 34. The output voltage of the digital-toanalog converter representing the product of the length of the strip which has passed between the rolls and the function of roll spacing versus length for the desired taper is transmitted through a line 35 to a summing amplitier 36 which also receives the output from a feedback potentiometer 37 representing the position of the Wedge 18 in the adjusting device 16. Consequently, the output from the amplitier 36 represents any change in roll spacing required to maintain the desired taper as the strip 15 passes between the rolls 11 and 12, and this output is transmitted by the line to the adjusting device 16.

When the strip has left the rolls after each pass, a force detector 38, such as an A.S.E.A. Pressductor, detects the reduction in stand force and transmits a signal through a line 39 to energize the relay 33, opening the contact 32 and closing a normally open contact 40. As a result, the tachometer is disconnected from the counter 24 and a continuously running clock 41 is connected in its place.

In operation, the input data T1, T2, and K are fed into the computer 22, which calculates the taper rate and provides a constant output voltage in accordance therewith. This taper rate is then compensated for any variation in the working rolls via the potentiometer 31 so that the voltage on the line 35 is proportional to the wedge adjustment needed for each fraction of roll rotation. As the strip 15 enters the mill stand 9, the force detected by the gage 38 de-energizes the relay 33, connecting the pulse tachometer 25 to the counter 24. The output of the counter is then converted to analog form and multiplied by the computer output in the digital-to-analog converter 23 to provide an output signal representing the required separation of the rolls. This signal, compared with the actual separation signal from the potentiometer 37, produces an error signal which commands the ram 17 to drive the wedge 18 to the required position. After the strip has left the stand, the force gage 38 ener-gizes the relay 33, causing the clock 41 to drive the counter, providing a continuously increasing output from the digitalto-analog converter. This action continues until the ram actuated wedge 18 has reached the end of its stroke, at which time the clock is disconnected, the counter is set up to count down and a signal is sent to the command console that the system is ready for the next pass. In the meantime, the screwdown mechanism 21 is adjusted so that the reduction in thickness to be produced in the next pass in accomplished entirely by operation of the Wedge 18.

In the arrange-ment shown in FIG. l, it has been assumed that the frame 10 of the stand is not deflected by the force constrained in the stand so that the position of the wedge 18 is always directly proportional to the separation of the working rolls 11 and 12 for any setting of the screwdown device 21. In practice, however, the stand is usually deected to an appreciable extent the magnitude of the deection being in proportion to the constant force and the modulus of elasticity of the stand.

Accordingly, to assure accurate rolling of the strip 15, the input thickness control signals T1 and T2 should incorporate a factor compensating for the stand deflection. This is accomplished by the compensating unit 42 shown in FIG. 2 wherein the desired thick and thin end dimensions Tg and T1 for a given pass of the strip are applied to two inputs 43 and 44 and the forces constrained in the stand at the thick end of the strip and at the thin end of the strip F2 and F1 divided by the stand modulus M are applied to two further input conductors 45 and 46, respectively. A summing amplifier 47 produces an output signal representing the change in stand deiiection from the beginning to the end of the pass and a switch 48 applies this correction signal to either of two further summing amplifiers 49 and 50, depending upon the direction of the pass. If the strip is moving through the stand in the direction from the thick end to the thin end, the switch 48 is in the position shown in FIG. 2. This applies the signal representing the change in stand deflection to the amplifier 50 where it is combined with the signal T'1 representing the desired final thickness, the stand deilection for the initial force being incorporated into the T2 setting. If the strip is moving in the direction from the thin end to the thick end, the switch 48 is moved to the opposite position applying the signal representing the change in stand detiection to the ampliiier 49 where it is combined with the desired final thickness value Tz to produce the corrected control signal T2.

It will be understood by those skilled in the art that the above-described embodiment is meant to be exemplary in that it is susceptible of modification and variation without departing from the spirit and scope of the invention. For example, the invention has been illustrated -using a pulse tachometer but measurement of the increments of length of the strip that passed between the rolls could also be accomplished with other devices. Furthermore, several diterent types of adjusting devices normally a part of the mill installation could be used. Therefore, all such variations and modiiications are included within the intended scope of the invention as set forth in the appended claims.

We claim:

1. Control apparatus for a rolling mill wherein a strip of material is passed between a pair of working rolls to reduce its thickness and including means for adjusting the separation of the working rolls in response to control s1 gnals to control the thickness of the material comprising measuring means for measuring the length of the material that has passed between the working rolls and producing an output signal corresponding thereto, computer means for producing a signal representing the required separation of the rolls at any point divided by the position of the point along the length of the strip to produce a desired taper and multiplier means for muliplying the outputs of the computer means and measuring means and transmitting to the adjusting means a control signal to actuate the adjusting means to produce the necessary roll spacing at the time the strip passes between the working rolls.

2. Control apparatus according to claim 1 wherein the means for measuring the length of the material that has passed between the rolls includes tachometer means providing output signals in proportion to the rotation of a working roll and counter means responsive to the tachometer means for producing an output voltage representing the accumulated rotation of the working roll and further including detecting means for determining when the strip of material has left the working rolls, switch means for disconnecting the tachometer means from the counter means when the material leaves the rolls, and clock means connected by the switch means to drive the counter means to a pre-selected position when the tachometer means is disconnected from the counter means.

3. Control apparatus according to claim 1 wherein the computer means includes input means for receiving signals representing the desired initial thickness and final thickness of the material and output means providing a signal related to the product of the sum and difference of the initial and nal thickness signals.

4. Control apparatus according to claim l including variable resistance means for manually altering the output signal from the computer means in accordance. with observed changes in the diameter of the working rolls.

References Cited UNITED STATES PATENTS 2,655,823 10/1953 Cozzo 72`ll 2,687,052 8/1954 Zeitlin 72-9 3,081,652 3/1963 Wright et al. 72-8 3,081,653 3/1963 Kincaid 72-8 CHARLES W. LANHAM, Primary Examiner. A. RUDERMAN, Assistant Examiner. 

